光捕集アンテナ系クロロゾームを構築するバクテリオクロロフィル類の生合成段階で働く酵素BciCの基質特異性とその反応機構の解明

Abstract

Green photosynthetic bacteria, one of chlorophotosynthetic species, have the largest and most efficient light-harvesting antenna systems (chlorosomes). The core part of chlorosomes comprises special bacteriochlorophyll-c/d/e pigments, which self-aggregate to form large oligomers. In the biosynthetic pathway of these pigments, a BciC enzyme catalyzes the removal of C132-methoxycarbonyl group of chlorophyllide-a. The substrate specificities of in vitro BciC enzymatic reactions for the central metal and C132-alkoxycarbonyl group, and the reaction mechanism were elucidated in the molecular level. The BciC would bind to the central metal to form the stereospecific complex. Additionally, the cavity in the active site of the BciC was predicted to be smaller than molecular size of zinc chlorophyll derivative bearing a propyl-esterifying group. Most importantly, the BciC would catalyze two-step reaction via hydrolysis by E85/D180 and decarboxylation by H137.